A monitoring device have been proposed which determines whether or not a driver is in a dangerous state, for example, looking aside or drowsing, and which alerts the driver when the driver is determined to be in a dangerous state. For example, the driver monitoring device disclosed in Patent Literature 1 determines, based on an image taken by photographing a pattern of bright spots projected on the face of a driver, angles of inclination of the driver's face when the driver turns his/her face up or down or left or right or when the driver otherwise inclines his/her face. Based on the angles of inclination of the driver's face determined, the device disclosed in Patent Literature 1 determines whether or not the driver is in a dangerous state, for example, looking aside or drowsing and, when the driver is determined to be in a dangerous state, alerts the driver.